Very Interesting, something I learned today
Project Habakkuk or Habbakuk (spelling varies; see below) was a plan by the British in World War II to construct an aircraft carrier out of Pykrete (a mixture of wood pulp and ice), for use against German U-boats in the mid-Atlantic, which was out of range of land-based planes.
http://en.wikipedia.org/wiki/Project_Habakkuk